How much does a loft conversion cost?
Loft conversions vary widely by type. Get an indicative all-in figure below, then build the works into a costed schedule.
What a loft conversion involves
- 1Structure and access
New floor joists, dormer/roof alterations and a compliant staircase.
- 2Insulation and services
Warm-roof insulation, plus electrics, heating and often an en-suite.
- 3Planning and party wall
Check permitted development vs planning, and serve party wall notices where relevant.
A loft conversion is one of the most reliable ways to add a bedroom (and value) to a terrace or semi — and for an HMO it can add a lettable room. The key is whether the uplift in GDV or rent beats the build cost, which the appraisal models.
Loft conversion costs by type (indicative)
| Type | Description | Indicative cost |
|---|---|---|
| Rooflight (Velux) | No structural extension | £20,000 – £35,000 |
| Dormer | Adds head height & floor | £30,000 – £55,000 |
| Hip-to-gable | End-terrace / semi | £40,000 – £65,000 |
| Mansard | Most space, most cost | £45,000 – £75,000+ |
All-in incl. structure, insulation, fit-out and stairs. Excludes furnishings.
Frequently asked questions
How much does a loft conversion cost?+
A dormer loft conversion typically costs £30,000–£55,000 all-in; rooflight conversions are cheaper and hip-to-gable/mansard cost more. It adds a lettable room and floor area.
Does a loft conversion add value?+
Adding a bedroom (with head height and proper access) usually lifts the valuation — model the uplift against the cost in the appraisal before committing.
Related tools & guides
Want to know how these figures are calculated? See our cost methodology.
Cost figures shown are indicative estimates, not quotations. You are responsible for verifying all costs (obtain contractor quotes) and any figures submitted to a lender. ScopeWise is a documentation tool, not financial, tax, structural or planning advice. HMO compliance prompts are guidance only — confirm requirements with your local council, as standards and licensing vary by authority.